Significant voltage fluctuations on device output

Support
1

Hello,
I have been trying to use otii arc to emulate battery and evaluate and model charging characteristic. I am however having problem with getting any sort of trustworthy data from the device.
DUT is prototype of wearable device, that has really tiny battery (10mAh LiPo, about 10ohm internal resistance). No matter what I try, either using otii in normal power box mode or battery emulation mode, I am getting really bad performance from the device in terms of voltage stability.

DUT does have HRV sensor that is connected directly to unregulated system power supply rail - that is effectively “direct” connection to battery via charger IC. Understandably - since HRV sensor draws current in short pulses, there is expectation to see some ripple/voltage dips on the rail.

However, despite device being able to supply much higher current, than pulses that device generates, voltage stability is downright terrible! I am seeing voltage fluctuations and ripple anywhere between 0.4V-2V (depending on measurement bandwidth of control device/oscilloscope) at average current being in 100-500uA range with pulses going up to 40mA (pulses are in 100-200us range).

Otii on its own sees fluctuations of 0.2-0.6V which is obviously result of lower bandwidth.

Since DUT uses linear charger IC (with max current capability of 10mA) using Otii to emulate battery (which I have successfully profiled) doesn’t create good charging characteristic as charger is trying to track voltage fluctuations with its current.

I tried using 2 otii arc devices - same result.
I tried otii 3 software and otii 2 software (with firmware change inbetween of course) - same result.

I tried using actual battery to power, using random bench power supply, as well as Nordics PPK powered directly from USB - they have all performed significantly better than otii in terms of voltage stability.
Of course, those other power sources don’t give me easy ability to emulate battery in a way that I could easily save and evaluate charging curve.

Since device will need to evaluate battery charge via voltage measurement only, this is making any sort of verification of firmware state of charge estimation algorithms using battery emulation mode pretty much impossible.

Please advise, and thank you for your response.
Matjaž

2

Hi Matjaž and welcome to the forum.

It sounds like that there is a short current pulse that triggers a range switch of the Arc.
You can try if this is the case by changing from Auto range to High range for Main current.

Easiest way to support you going forward is if you create a case in our case system and share an Otii 3 project there, showing the behavior.
https://www.qoitech.com/cases

Best regards,
Björn

3

Thank you!
Changing to High range did help stabilize the voltage!
May I suggest improvement for Otii software that could help avoid confusion with that:
Could there be some sort of mechanism implemented, that if frequent switching of current range is detected during measurements it would throw notification about this? As main current range setting is in most cases “no need to touch” setting it would be cool to be notified when it might be an issue. Just suggestion of course :slight_smile:

4

Hi,

Thank you for this feature request, it is appreciated!

Best regards,
Björn